Overspeeding baldor motor drive

[Katy1163]

I am wondering if anyone knows how to overspeed a baldor motor using a baldor inverter control. It is currently running at max 1700rpm and i need it to run at 2400rpm. I am sure it can be done because I have contacted baldor and they said it is possible. Now I just need to figure out how.....

Thanks!!

 

[DickDV]

You need to go into the drives software and find the parameter that controls maximum speed or maximum frequency. If speed, set it up to 2400rpm, if frequency, set it up to 81Hz.

You may find after making these changes that the drive does not increase in speed to the intended level.

If that happens, again go into the drive software and look for another parameter that sets the maximum frequency or speed for the speed reference. It also might be called max speed or frequency for the analog input that you are using for your speed signal. Change that up to the same level as above.

If that doesn't do it, probably should give us the drive brand and model number so we can be more specific about which parameters to change.

 

[ozmosis]

You also need to ensure your application will allow overspeeding. Certain applications, such as centrifugal loads will produce more power as the speed increases but your inverter will only be able to supply the rated power.
I'm a little curious as to why Baldor didn't actually tell you how to do it when they informed you it was possible. Seems odd.

 

[Katy1163]

The drive that I am using is a baldor inverter control Series 15H, cat # ID15H205-E. I am not personally the one who talked to Baldor. My boss just told me that he talked to them and it was possible and told me to figure out how. I can't understand why, when asking them if it possible, he didn't ask how. Anyway, what it is being used for is a training unit for a wind tunnel. The drive is controlling the motor, which in turn controls the fan speed. We need to increase the fan speed to get the air velocity up to spec. I, myself, am not too experienced with motor drives, so any help I could get would be appreciated.

 

[itsmoked]

Make sure the fan blades are rated for that speed as the centripetal forces will go up substantially. Wouldn't want a blade through someones chest.(training gone bad)

I think sed2developer meant to say "centrifugal loads will [red]consume[/red] more power". Possibly a lot more power!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Warpspeed]

You will need to beg, borrow, or steal the correct operating handbook for the particular drive you are using. That should contain all the information you need to reprogram the drive to operate up to a higher output frequency.

As stated above, you will be moving a lot more air at a higher differential pressure, and the motor will need to produce a lot more horsepower to do that. But how much depends on the particular fan characteristics. Monitor motor amps on the drive, and don't let it get above the full load amps specified on the motor rating plate.

Typically motor power increases between square law, and cubed law with Rpm, so the Hp increase is likely going to fall somewhere between x2.5 and x4.0 If the motor is already nearly fully loaded, it may not be terribly happy with up to a 400% potential increase in load.

Wise words from Keith about fan blade speed too, and also be aware of the speed rating of the motor bearings, but I very much doubt that will be a problem. It is just something to keep in mind.

 

[waross]

HelloWarpspeed
I did some research on bearings and found that some manufacturers use the same bearings for 3600 RPM service as for 1800 RPM service. The service interval is shorter at higher speeds.
respectfully

 

[Warpspeed]

Funnily enough I am looking at a 15 Hp 2,900 rpm motor right now, that will be run intermittently at up to 5,800 rpm. The bearings (6209) are rated to 5,300 Rpm continuous with standard grease lubrication.

This is for a high pressure large diameter centrifugal blower. this blower originally came fitted with a 1.5Hp motor. At double the Rpm it generates four times the pressure and almost twice the mass flow, requiring eight times the drive horsepower. It is unfortunately one of those cubed law beasts, and VERY power hungry.

It will be run with a VSD, and will rarely see full Rpm, and then only for very short intervals. The bearings hopefully should be up to the job.

 

[CJCPE]

If you don't have the manual, you can download it from Baldor at

http://www.baldor.com.

To get the required output frequency, I think that all you need to do is increase the setting of the MAX Output Frequency parameter in the Output Limits group of parameters.

The drive will provide 81 Hz output with no problem, but the output voltage will be proportional to output frequency only up to 60 Hz. Above 60 Hz, the output voltage will remain at the 60 Hz value. That means that the torque capability will be reduced above 60 Hz such that torque times speed is a constant value. At 81 Hz, the torque available for rated motor current will be about 75% of rated.

As pointed out above, the torque required to operate the fan at 2400 RPM will be about twice the torque required at 1700 RPM. The increased load combined with the reduced motor capability will mean that the rated torque of the motor will be exceeded at 2400 RPM if the torque required at 1700 RPM is more than about 37% of rated motor torque.

 

[jraef]

A critical issue that has been alluded to but not expressly stated is this:
As the frequency output increases from the VFD, the voltage will be at maximum, so the motor horsepower WILL REMAIN CONSTANT! Torque will therefore drop precipitously as you increase speed. Most likely, unless your motor is grossly over sized to operate at the speed it is now running, it WILL NOT WORK. Your motor will overload very quickly.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[Skogsgurra]

That "constant power above base speed" statement needs to be expanded on a bit.

What happens is that your motor voltage stays constant as you move above the base speed (usually 50 or 60 Hz). So your V/Hz figure goes down as frequency goes up.

That doesn't immediately mean that your torque drops. But, the maximum available torque drops. And not inversely proportional to frequency, but inversely proportional to frequency squared.

This has two implications.

First, the slip increases, so the rotor gets hotter. But cooling increases, too. So you can still usually get the same torque even if you increase speed about ten percent. It all depends on what rotor you have.

Second, when frequency is increased so that peak torque comes down to the load line, the motor just stalls. Nothing more to do.

The range between rotor getting too hot (at 10 perhaps 20 percent overspeed) and when motor stalls is a grey zone where anything can happen. Best bet is that life of motor gets reduced due to high temperature.

This is for a fan with torque proportional to speed squared. Other loads and motors with more spare torque behave otherwise.

Gunnar Englund

http://www.gke.org

 

[jraef]

OK Gunnar,
That's a much more thorough answer, but he is planning on running at 140% speed so he will be in that danger zone for sure. I also should have used the word Stall instead of Overload.

My experience with people overspeeding fans is that it rarely gives the results they were expecting and I thought it worthy of explaining to the OP before he embarks further without checking it out.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[Skogsgurra]

Yes, and they do not stall. They just don't increase speed any more if they have fan loads - which they have. You should have corrected me there. But you are the humble timid person you always were. ;-)

Gunnar Englund

http://www.gke.org

 

[jraef]

I once had an Aluminum Mill come to me with a project conceived by the Production Manager. He wanted to reduce the number of shutdowns required for cleaning the ventilation filter media over the pot lines. His brilliant idea was to use VFDs to increase the fan speed over rated design as the filters loaded up by monitoring the differential pressure across the filter. He assumed that by over speeding the fan it would maintain a constant air flow volume (the critical measurement) through a clogged filter for longer. No matter how much I proved to him that it wouldn't work, he insisted, and gave the order to a competitor. There were 64 x 75HP fans, but at least I convinced his subordinates to test his theory on one section with only 4 fans. Needless to say I was proved correct, but my competitor still got an order for 4 75HP VFDs and inverter duty motors. :-(

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[Skogsgurra]

That wasn't too bad. Only four drives. Or didn't the 6 "take"?

In that case - I would feel real angry.

Gunnar Englund

http://www.gke.org